1. Field of the Invention
This invention relates to a method and apparatus for blowing an optical fibre member.
2. Description of Related Art
A method is known from EP-A-108590 for installing an optical fibre member in a tubular passageway using a flow of air which travels along the tubular passageway in the desired direction of travel of the optical fibre member. For this purpose the optical fibre member comprises an outer sheath surrounding one or more optical fibres, the sheath being of low density so as to facilitate movement of the fibre member by the flow of air. One feature of the method and apparatus described in EP-A-108590 is that the optical fibre member is introduced into the tubular passageway through a pressurised blowing head via a seal, which must both allow the fibre member to pass through freely and must minimize the escape of air. To introduce the optical fibre member it passes between a pair of drive wheels located within the blowing head. The drive wheels engage the optical fibre member in the nip between the wheels and impart a longitudinal force to the optical fibre member in the direction of introduction
An object of the present invention is to provide a method and apparatus for introducing one or more optical fibre members into a tubular passageway which avoids the need for such drive wheels, avoids the need for a seal around the fibre where it enters the head and avoids viscous drag opposed to the direction of motion, downstream of the wheels. The avoidance of drive wheels is particularly advantageous in the case of optical fibre members which have only a single optical fibre in a flexible sheath, since such members may be so lacking in rigidity that applying an effective longitudinal force to them by means of drive wheels is difficult.